visitor Bob G. wrote to request help with identifying a Cox .020-powered
free flight model that he remembered seeing in an old edition of
American Aircraft Modeler. He couldn't recall the name for sure,
but gave a good enough description and a guess at the approximate
timeframe that I was able to find it for him - the "Mini-ROD." Bob
is planning on building a lot of the Tenderfoot series of models
that appeared monthly back in the era.
Note: Bob is also
building a "Chipper II"
free flight model.
by Bob Stalick
A size free-flight (020) that resembles today's
big-brother competition designs. Performs like them, too!
a sunny afternoon with a slight breeze, You unpack the Mini-Rod,
measure the fuel into the tank, connect the batteries, flip the
engine to life, light the dether-malizer fuse, and launch it into
the wind. When the engine stops 15 seconds later, your model is
a bright-colored speck in the sky silhouetted against the white
clouds. Then the fuse burns through the dethermalizer rubber band,
the stabilizer trailing edge pops up, and the Mini-Rod descends
slowly into the grass. If this picture stirs your imagination, you
can quickly build a good model from the plans on the next two pages.
Begin on Friday and fly it Sunday.
Mini-ROD, by Bob G.
Mini-Rod is the ideal
design for the new AMA-HIAA-Navy youth program as the time-target
free-flight model. This design was arranged so that you can make
your first model from the magazine plan. Mini-Rod is inexpensive,
costing less than $1.50 for materials (less engine). It can be built
in two forms. Choose the one you like better. It's rugged in all-balsa
form, but it performs better with the built-up wing.
has been flown with a number of engines from the 010 Tee Dee to
a tired old 045 Baby Spitfire. It seems happiest with the 020 Cox
Pee Wee or Tee Dee. One Mini-Rod was modified for Jetex 150 power!
The plans are straightforward, but before beginning to work,
obtain all the supplies in the Bill of Materials. Here are a couple
of hints for selecting the right kind of balsa wood to do the best
job. C-grain balsa - some call it quarter-grain - has a strange
mottled or freckled appearance with shiny spots. You will generally
find that the lightest and stiffest and strongest wood has this
grain. Pick it for wing spars, ribs, leading and trailing edges.
Use it where flat sheets are needed as it doesn't bend over curves
easily. A-grain balsa is identified by the grain streaks running
side-by-side the length of a sheet. It fits over curves - like airfoils
- and rolls into tubes nicely (and especially when wet). So look
over the wood rack. Choose first for strength and then for lightness.
Later on, you can shoot for light weight and compromise on strength.
Now that you have chosen the materials and readied tools, pick a
nice straight and flat work surface to pin your plans on. Cover
plans with waxed paper, then before you cut anything, read the plans
very care-fully. Notice that there are two different types of wings
shown. One is sheet balsa, the other is built-up and tissue-covered.
Be careful, don't try to build one wing panel of all balsa, the
other with ribs and spars. Even though Mini-Rod would probably fly
with this arrangement, it would be tough to trim out. For speed
and ease of construction, build the balsa sheet wing first.
Polyhedral wing - one with "double" dihedral - requires putting
dihedral in tip first, then center section. Sheeted wing shown
Here's how to put in that dihedral when you make the built-up
wing. Prop up the tips the required amount with wood scraps.
How the fuselage and wing mount go together. Text tells how
to assemble the mount flat on the bench. It's simple and really
Compare these details with pictures on opposite page to help
with construction of wing dihedral joints. Work slowly for accuracy.
This is how you glue in the ribs on the underside of the sheet-balsa
Use a ruler or similar object to bend the sheet as necessary
for this two-step operation.
1) Build the sheet wing
by gluing a 30" long 1/8 x 2 sheet of balsa to a similar length
of 1/16 x 3. Be certain that they are glued evenly and securely.
I recommend Sig-Bond or similar adhesive. Cut the tapered tip to
shape as indicated on the plans, and mark all the rib locations
directly on the underside of the wing. This is a good time to sand
the topside of the wing to get a good smooth surface joint. Preglue
all the ribs and the sheet where the ribs join. Glue in all ribs,
except at the dihedral joint, starting at the trailing edge on the
(on the 1/16sheet). Allow this to dry thoroughly. Before gluing
the ribs to the leading edge sheeting, dampen the topside with water
to allow the balsa to flex more easily, then pin the ribs to the
1/8 sheet and glue securely. After this assembly has completely
dried, cut the wing at the dihedral and polyhedral joints where
indicated, then with a large sanding block, sand the ends where
the panels join so that they fit when the angle is glued in. Preglue
and allow to dry. Glue the tip panels to the main panels, blocking
them up as indicated. After they have dried thoroughly, join the
two wing halves in a manner similar to that used on the tips.
Add the remaining ribs at the dihedral joints. After everything
has dried, reglue all ribs flush at the bottom of the wing. Add
optional cloth reinforcement at the dihedral joints. The stab is
constructed in a similar fashion, with the exception of the addition
of the hold-down hooks glued and sewn as indicated on the plans.
2) Construct the pylon next. Cut sheet size indicated and splice
edge-to-edge the two pieces used to form each side. Mark the location
and size of the 1/4 balsa strip pylon braces and glue into place.
Glue on the other pylon side to complete the structure. Don't glue
the pylon to the fuselage yet.
3) Fuselage: The fuselage
is simply a piece of 1/4 x 1/2 balsa cut to length and tapered at
the rear as indicated. Notice that the front has an additional piece
of 1/4 x 1/2 balsa glued to the top. Add the 1/8 x 1 x 1 plywood
firewall, after you have fitted your engine, drilled mounting holes
and glued the blind nuts into place. Add the balsa filler blocks
to the sides of the fuselage behind the firewall. Sand a groove
into the left side block so an eyedropper fuel tank can be installed.
Right here, a note would be in order to explain how the
eyedropper installation works. You will need to drill a 1/8 to 3/16
hole in the fuel tank of the Pee Wee (make sure you clean out the
metal filings from the tank), attach a length of small diameter
fuel line to the fuel nipple on the needle valve in the Pee Wee
tank. Attach the other end to the eyedropper. You can, in this simple
installation, visually check the amount of fuel remaining and have
a simple and effective fuel timer. Fix the eyedropper to the fuselage
by looping a rubber band around the fuselage and fastening it on
each end of the dropper.
Of course you can just estimate
the amount of fuel remaining in the Pee Wee tank and hope that the
model doesn't get too high on what you think you've got left - this
is what I did on the first flight of the model in the pictures.
Eight minutes later - no! I didn't light the D.T. (de-thermalizer)
fuse - it came down, thanks to cool air, at a good hiking distance
Glue the rudder onto the fuselage as indicated
on the plans, notice the cutout at the trailing edge. This serves
as a stop for the pop-up action of the stab when dethermalized.
Glue on the stab platform.
4) After all component parts
are completed, trim with colored tissue and give the whole structure
three coats of clear dope. Install the engine, prop, stab. Fasten
the wing to the pylon with a couple of rubber bands and you are
ready for test gliding.
5) Test gliding and flying: Pin
or tape the into position and test glide. Move the forward or back
until a good glide, no diving or stalling tendencies, is evident,
then glue pylon into place on the fuselage. It may be necessary
to raise the front of the pylon somewhat if your model is nose-heavy,
or to raise the back of the pylon somewhat if your model is tail-heavy.
Try to keep the balance point as indicated on the as close as possible.
You are now ready for powered flight. As most pylon models,
this one has a normal right power pattern. The model should launched
at a 45-degree angle into the wind and should climb in loose right
spirals until the engine cuts, then it should drift into a tight
Additional glide turn can be achieved by
packing the stab platform so that the right when viewed from the
rear, is higher than the right tip. If the model tends to loop,
a small amount of down-thrust (engine tilted down) by inserting
washers behind the two top bolts between the tank mount and the
After you have had a few successful may
wish to build the optional built-up wind as shown on the plans.
This wing is identical in size and shape to the balsa wing, but
it has the additional advantage of a more efficient airfoil and
lighter weight. Transfer the wing rib shapes onto plywood or stiff
cardboard and using these as guides, cut out the indicated number
of ribs. Cut the leading and trailing edges to shape and pin into
place. Lay the spar onto the plan and glue in the ribs where indicated,
after you have notched the trailing edges to receive the wing ribs.
Additional details on this type of wing construction can be found
in the Jan. '68 issue of A.A.M., in the article "Get Into Free Flight."
built-up wing can be substituted for the all-balsa wing, although
some changes will be necessary in the wing angle due to the increased
lift of this wing ..
Some suggestions: Build the model
with the sheet wing first, then, for a surprising improvement in
performance, build the built-up wing.
Always put your
name, address, phone number and AMA number on your model. Build
your model as lightly as possible for better performance. The model
in the article weighed 2-3/4 ozs., ready-to-fly in the all-balsa
form, and just under 2-1/2 ozs. in its built-up-wing version.
Always use a fuse to dethermalize your model, even
on test flights, as even models of this type can be lifted high
into the sky with a little bit of thermal assistance.
Good luck and many happy flights with your Mini-Rod. Let us know
how it flew for you.
2 - 1/16 X 3 X 36" balsa sheets for stab,
fin, wing ribs and sheeting and pylon sides
1 - 1/8 X 3 x 36"
balsa sheet for wing leading edge and ribs
1 - 1/4 sq. x 36"
balsa strip for pylon frame and wing hold-down
1 - 1/4 x 1/2
x 36" balsa strip for fuselage
1 - 1 x 1" pc. of 1/8" thick
plywood (In addition, if you plan to make the built-up wing version,
the following wood will be needed.)
1 - 1/8 x 1/4 x 36" balsa
strip for wing spar
1 - 1/8 x 1/2 x 36" balsa trailing edge
1 - 3/16 sq. x 36" balsa strip for wing leading edge
4 - 2-56 blind mounting nuts for engine mount
4 - 2-56 x
3/8 or 1/2" mounting bolts 3 - paper clips for misc. hooks
1 - sheet Silkspan or Jap tissue
gauze or other joint-reinforcing fabric; glue; pins; dope and brushes
<click for larger
The AMA Plans Service offers a
full-size version of many of the plans show here at a very reasonable cost. They
will scale the plans any size for you. It is always best to buy printed plans because
my scanner versions often have distortions that can cause parts to fit poorly. Purchasing
plans also help to support the operation of the
Academy of Model Aeronautics - the #1
advocate for model aviation throughout the world. If the AMA no longer has this
plan on file, I will be glad to send you my higher resolution version.
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Posted January 10, 2012